1. Field of the Invention
The invention relates to a brushless motor for rotating a recording medium such as CD-ROM, DVD, and DVD-ROM to which data is written at a constant line density so that a constant amount of data is written and read per unit time. More particularly, it relates to a driving circuit for a three-phase brushless motor.
2. Description of the Prior Art
FIG. 30 shows a configuration of a generally known reproducing equipment having an optical disc such as CD-ROM as a recording medium, whose main circuit is integrated into a semiconductor integrated circuit apparatus.
In FIG. 30, a CD-ROM loader 100 comprises a driving system as well as a reading system which are used mainly for reading data stored in the above-mentioned recording medium, such as a spindle motor for rotating a recording medium to which data is stored at a constant line density, a location detector comprising a Hall effect sensor and so on for detecting a rotating location of this spindle motor, a light pick-up for reading out data stored in the recording medium, and a light pick-up driving system for driving this light pick-up along the recording medium.
A motor driving circuit 200 drives and controls the spindle motor in the above-mentioned CD-ROM. The motor driving circuit 200 to which the present invention relates is described in detail below. A DSP 300 comprises a control signal generator for giving a motor control signal (EC) and reference voltage (ECR) to this motor driving circuit. An actuator driving circuit 400 drives and controls the light pick-up driving system in the CD-ROM loader. A controller 600 comprises a microprocessor for giving various kinds of control signals to the motor driving circuit 200, the DSP 300 and the actuator driving circuit 400.
In the data reproducing equipment constructed as mentioned above, the rotating speed of a disk body (recording medium) is controlled so that data (stored information) is written at a constant line density on the disk track of the recording medium and a constant amount (constant line speed) of data is read out per unit time when the data written in the recording medium is reproduced.
In other words, in order to take out a data written on a certain track of the recording medium, the rotating speed of the recording medium is required to be controlled in accordance with the location of the track where the data is stored.
The recording medium is rotated by a small DC motor, namely, a spindle motor. With regard to a structure, the spindle motor is roughly classified into the following two types according to the difference in the reproducing equipment in which the spindle motor is installed. One of the types is a single phase brush motor whose motor rotating speed varies in the range of approximately 200.about.500 rpm, which is often installed in a reproducing equipment having a relatively lower speed range for controlling a rotating speed. The other is a three-phase brushless motor which is often installed in a reproducing equipment such as a CD-ROM where data is processed in a high speed and the motor rotating speed is controlled in a relatively faster speed range. FIG. 31 shows a relationship between the track location of the recording medium and the rotating speed in an eight-times speed CD-ROM reproducing equipment, for example, in which the three-phase brushless motor is used.
Referring to FIG. 32, the following explains on a motor driving circuit, in case that a three-phase brushless motor is used as a spindle motor for rotating a recording medium such as CD-ROM where recording is done at a constant line speed.
In FIG. 32, a three-phase brushless motor main body 11 (spindle motor main body) rotates a recording medium (not illustrated) where recording is done at a constant line density according to the relationship between the track location and the rotating speed, as shown in FIG. 31, for example. The three-phase brushless motor comprises motor coils of U phase, V phase and W phase.
Location detection Hall effect sensors 12.about.14 are provided for the U phase, V phase and W phase, corresponding to the motor coils of these U phase, V phase and W phase in the three-phase brushless motor main body 11. A power supply 15 is provided for driving the motor.
A power supply electric potential node Vcc and an earth electric potential node GND are connected to the power supply 15. These Vcc and GND are power-supply terminals connected to a semiconductor integrated circuit apparatus comprising the motor driving circuit 200. A motor control signal (EC) from the DSP 300 and reference voltage (ECR) are inputted respectively into a control signal input node EC and an reference electric potential node ECR in a semiconductor integrated circuit apparatus comprising the motor driving circuit 200, respectively.
Location detection signal input nodes Hu+, Hu- of the U phase, Hv+, Hv- of V phase and Hw+, Hw- of W phase are connected to the location detection Hall effect sensors 12.about.14 of the corresponding phases of the semiconductor integrated circuit apparatus which is comprising the motor driving circuit 200. Output nodes U, V and W supply currents from the semiconductor integrated circuit apparatus comprising the motor driving circuit 200 to the motor coils of the respective U, V and W phases of the three-phase brushless motor main body 11.
Power-supply side output power transistors 1.about.3 are connected between the power supply electric potential node Vcc and the corresponding one of the output nodes U, V, and W in correspondence to respective U, V and W phases. In this case, respective power-supply side output power transistors consist of NPN bipolar transistors whose collector electrodes are connected to the power supply electric potential node Vcc, whose respective emitter electrodes are connected to the corresponding output nodes U, V and W.
Respective ground side output power transistors 4.about.6 are connected between the corresponding output nodes U, V, and W and a common node in correspondence to respective U, V and W phases. In this case, respective earth side output power transistors consist of NPN bipolar transistors whose collector electrodes are connected to the corresponding output nodes U, V and W, whose emitter electrodes are connected to the common node.
Parasitic diodes 7.about.9 appear between the earth electric potential node and respective output nodes U, V and W, when a motor output decreases to less than earth electric potential in case of applying a reverse torque to the spindle motor and so on (for example, in case of motor braking). The parasitic diodes are formed by the earth side output power transistors 4.about.6, namely, by PN junction of a semiconductor substrate (generally at the earth electric potential) where these transistors 4.about.6 are defined and the collector regions of these transistors 4.about.6.
A detection resistor 10 detects current flowing in the motor coils of the spindle motor main body 11. The detection resistor 10 is connected between a common node to which the earth side output power transistors 4.about.6 are connected and the above-mentioned earth electric potential node.
An absolute value circuit 16, whose pair of input nodes are connected to the reference electric potential node ECR and the control signal input node EC, calculates the difference between the control signal (EC) inputted to the control signal input node EC and the reference voltage (ECR) inputted to the reference voltage node ECR, for outputting an absolute value of the arithmetic result, .vertline.EC-ECR.vertline..
An output current controller 17 comprises an amplifier which receives an output signal from the absolute value circuit 16 for providing current multiplied by a predetermined gain of the received output with both the power-supply side output power transistors 1.about.3 and the earth side output power transistors 4.about.6. The output current controller 17 consists of a comparator. An inverting input terminal (-) of the comparator is connected to the common node to which the emitters of the respective earth side output power transistors 4.about.6 are connected. A non-inverting input terminal (+) of the comparator is connected to the output terminal of the absolute value circuit 16. The comparator outputs a first output, which is a differential voltage between the electric potential inputted to the non-inverted input terminal (+) and the electric potential inputted to the inverted input terminal (-), to the first output terminal. The comparator outputs a second output which is an inverted first output to the second output terminal.
A switching signal generator 18 consists of a comparator and outputs a switching signal which is made in accordance with a difference between the motor control signal (EC) inputted to the control signal input node EC and the reference voltage (ECR) inputted to the reference electric potential node ECR. A non-inverted input terminal (+) of the comparator is connected to the control signal input node EC, and an inverted input terminal (-) of the comparator is connected to the reference electric potential node ECR. When the potential of the motor control signal (EC) is lower than the reference voltage (ECR), the comparator outputs "L" level switching signal which shows an accelerating mode. When the potential of the motor control signal (EC) is higher than the reference voltage (ECR), the comparator outputs "H" level switching signal which shows a decelerating mode.
A switching control signal generator 19 outputs a switching signal for deciding a switching state of both the power-supply side and the earth side output power transistors 1.about.6 in the next timing in accordance with the motor location signal from the location detection Hall effect sensors 12.about.14 and the switching signal from the switching signal generator 18. The switching control signal generator 19 comprises input nodes connected to the location detection signal input nodes Hu+, Hu-, Hv+, Hv-, Hw+ and Hw-, and three output nodes corresponding to respective U, V and W phases.
A power-supply side controller 20 comprises a pre-driver circuit. The pre-driver circuit receives a switching control signal from the switching signal generator 19 and the first output current from the output current controller 17. According to a switching state decided according to the received switching signal, the pre-driver circuit supplies a current, which is multiplied with the first output current and the received predetermined gain, to the power-supply side output transistors 1.about.3 as a base current.
A power-supply side controller 21 comprises a pre-driver circuit. The pre-driver circuit receives a switching control signal from the switching signal generator 19 and the second output current from the output current controller 17. According to a switching state decided according to the received switching signal, the pre-driver circuit supplies a current, which is multiplied with the second output current and a predetermined gain, to the earth side output transistors 4.about.6 as a base current.
Referring to FIGS. 33(a)-33(c) and FIG. 34, the operation of the motor driving circuit constructed as mentioned above is explained below. FIG. 33(a), FIG. 33(b), and FIG. 33(c), respectively; show relationships among the motor rotating speed (disc rotating speed), coil current of the motor, and output voltage of the motor, when a recording medium such as the CD-ROM of FIG. 33(a) is driven. FIG. 34 is a timing chart showing the motor control signal WC) and the reference voltage (ECR) when the state is changed from an accelerating mode to a decelerating mode, the motor location signals (hole sensor signal) from the location detection hole sensors 12.about.14, the switching state of both the power-supply side and the earth side output power transistors 1.about.6, and the coil current of the motor.
Referring to FIGS. 33(a)-33(d), an operation of the motor driving circuit is outlined as follows. In FIG. 33(a), section A is a section in which a light pick-up on each track on the recording medium reads out or writes data by one by one, which section is abbreviated to a read-out period. Section B is a section in which the light pick-up moves from a track at the outer circumference to another track at an inner circumference by skipping the tracks therebetween (abbreviated to an accelerating moving period). The section A and the section B are referred to as accelerating moving periods or decelerating mode periods. Section C is a section in which the light pick-up moves from a track at the inner circumference to the track at an outer circumference by skipping the tracks therebetween. Section C is abbreviated to a decelerating moving period or a decelerating mode period.
Section A
In this section A, the motor control signal (EC) inputted to the control signal input node EC is at "L" level, as shown in the accelerating mode in FIG. 34. During the section A, a switching signal is therefore given from the switching signal generator 18 to the switching control signal generator 19 so that the current flows in the direction to generate a forward direction torque (forward torque) to the motor coils of the spindle motor main body 11.
The location detection Hall effect sensors 12.about.14 give electric potential to the location detection signal input nodes Hu-, Hv+, Hv-, Hw+ and Hw- so that the electric potential between Hu+ and Hu-(Hu+!-Hu-!), the electric potential between Hv+ and Hv-(Hv+!-Hv-!) and the electric potential between Hw+ and Hw-(Hw+!-Hw-!) show switching state signals for the respective U, V and W phases, which are shown as approximate sign curves whose phase are shifted by 120 degrees to each other, as shown in FIG. 34.
Accordingly, receiving a switching signal from the switching signal generator 18 and a switching state signals given to the location detection signal input nodes Hu-, Hv+, Hv-, Hw+ and Hw-, the switching control signal generator 19 gives a switching control signal which generates a forward torque in the motor to both the power-supply side controller 20 and the earth side controller 21.
In accordance with the current value according to the first and the second outputs form the output current controller 17, the power-supply side controller 20 and the earth side controller 21 give respective base currents corresponding to the received switching control signals to the respective power-supply side and the earth side output power transistors 1.about.6.
Accordingly, the power-supply side and the earth side output power transistors 1.about.6 are on/off controlled as shown in FIG. 34.
As a result, the current flows from the power supply 15 to the electric potential node GND, via the power supply electric potential node Vcc, either one of the power-supply side output power transistors 1.about.3, either one of the output nodes U, V, W, the motor coils of the spindle motor main body 11, either one of the output nodes U, V, W, either one of the earth side output power transistors 4.about.6 and the detection resistor 10 according to the on/off of respective output power transistors 1.about.6 of the power-supply side and the earth side. That is, the coil current of the motor flows as the currents Iu, Iv, Iw as shown in FIG. 34, which generate forward torques and the motor rotates in the forward direction.
Since this section A is a read-out period, the light pick-up moves toward an inner track one by one. As shown in FIG. 33(b), the rotating speed of the motor is gradually raised according to the location detection signal from the location detection Hall effect sensors 12.about.14.
However, as shown in FIG. 33(d), the output voltage of the motor does not increase significantly due to a slow motor rotating speed. In other words, a large ratio of voltage is applied to the motor driving circuit. However, since the load of the motor is very small, currents flowing in the coils of the motor are also very small as shown in FIG. 33(e). In other words, the power consumption of the motor driving circuit is relatively small.
Section B
Since this section B is also the accelerating moving period as well as the section A, the motor driving circuit is driven so that a forward torque is generated in the motor. In other words, according to the location detection signal from the location detection Hall effect sensors 12.about.14, the coil currents Iu, Iv, Iw of the motor flow in the directions as shown in FIG. 34 from the power supply 15 to the electric potential node GND, via the power supply electric potential node Vcc, either one of the power-supply side output power transistors 1.about.3, either one of the output nodes U, V, W, the motor coils of the spindle motor main body 11, either one of the output nodes U, V, W, either one of the earth side output power transistors 4.about.6 and the detection resistor 10. Receiving a forward torque, the motor rotates in the forward direction.
However, since this section B is the accelerating moving period, the rotating speed of the motor is raised, compared to that in the section A. As shown in FIG. 33(d), the output voltage of the motor is increased and a small ratio of voltage is applied to the motor driving circuit. However, since the load of the motor is large, currents flowing in the coils of the motor are relatively large as shown in FIG. 33(e). Accordingly, the power consumption of the motor driving circuit becomes larger than that in the section A.
Section C
The section C is the decelerating moving period. As shown in the decelerating mode in FIG. 34, the motor control signal (EC) inputted to the control signal input node EC changes to "H" level. Then, a switching signal is applied from the switching signal generator 18 to the signal switching control signal generator 19 so that the currents flow in the direction to generate a reverse torque in the motor coils of the spindle motor main flame 11.
The location detection Hall effect sensors 12.about.14 give electric potential to the location detection signal input nodes Hu-, Hv+, Hv-, Hw+ and Hw- so that the electric potential between Hu+ and Hu-(Hu+!-Hu-!), the electric potential between Hv+ and Hv-(Hv+!-Hv-!) and the electric potential between Hw+ and Hw-(Hw+!-Hw-!) show switching state signals for the respective U, V and W phases, which are shown as approximate sign curves whose phase are shifted by 120 degrees to each other, as shown in FIG. 34.
Accordingly, receiving a switching signal from the switching signal generator 18 and a switching state signals given to the location detection signal input nodes Hu-, Hv+, Hv-, Hw+ and Hw-, the switching control signal generator 19 gives a switching control signal which generates a forward torque in the motor to both the power-supply side controller 20 and the earth side controller 21.
In accordance with the current value according to the first and the second outputs form the output current controller 17, the power-supply side controller 20 and the earth side controller 21 give respective base currents corresponding to the received switching control signals to the respective power-supply side and the earth side output power transistors 1.about.6.
Accordingly, the power-supply side and the earth side output power transistors 1.about.6 are on/off controlled as shown in FIG. 34.
As a result, the current flows from the power supply 15 to the electric potential node GND, via the power supply electric potential node Vcc, either one of the power-supply side output power transistors 1.about.3, either one of the output nodes U, V, W, the motor coils of the spindle motor main body 11, either one of the output nodes U, V, W, either one of the earth side output power transistors 4.about.6 and the detection resistor 10 according to the on/off of respective output power transistors 1.about.6 of the power-supply side and the earth side. That is, the coil current of the motor flows as the currents Iu, Iv, Iw as shown in FIG. 34, which generate reverse torques and the rotating speed of the motor is lowered, namely, decelerated as shown in FIG. 33(b).
In this section C, the rotating speed of the motor is lowered, the output voltage of the motor is not raised significantly as shown in FIG. 33(d), and the coil current of the motor flows until it reaches the limit current value of the motor driving circuit.
Accordingly, the power consumption of the motor driving circuit is significantly larger than those in the sections A and B.
Referring to FIG. 34, the switching timing from the accelerating mode to the decelerating mode is explained in detail as follows.
Since the motor control signal (EC) changes from (EC)&lt;(ECR) to (EC)&gt;(ECR) in reference to the reference voltage (ECR), the mode changes from the accelerating mode to a decelerating mode. At this time, the power-supply side and the earth side output power transistors 1.about.6 are on/off controlled according to the switching signal from the switching signal generator 18 so that the output power transistors 1.about.6 are switched in a reverse sequential order than before, by means of the signal generator 19, the power-supply side controller 20 and the earth side controller 21, as shown in FIG. 34
Accordingly, the motor coil currents Iu, Iv, Iw flow reversely than before, as shown in FIG. 34. In other words, this generates a reverse torque in the motor, which gives braking on the motor and decelerates the motor.
The current flow around the output stage of the motor and the motor driving circuit, during entering the acceleration mode and changing to the decelerating mode, and again entering the accelerating mode after the motor is started, is explained below using FIG. 35.about.FIG. 41. To make the explanation simple, the following explanation focuses on the current flow between arbitrarily chosen two outputs in the motor, namely, between the output nodes U-V, for example.
When the motor is started (accelerating mode), the motor control signal (EC) becomes lower than the reference voltage (ECR), as shown in FIG. 41. The respective power-supply side and the earth side output power transistors 1.about.6 are on/off controlled so that a forward torque is generated in the motor.
It is assumed now that the power-supply side output power transistor 1 and the earth side output power transistor 5 are on, and the rest of the transistors are off.
As shown in FIG. 35 CASE 1!, the motor coil current IL flows from the power supply 15 to the earth electric potential node GND via the power supply electric potential node Vcc, the power-supply side output power transistor 1, the output node U, the motor coils of the spindle motor main body 11, the output node V, the earth side output power transistor 5, and the detection resistor 10.
At the start of the motor, the back electromotive voltage (VBEMF) induced in the coils of the motor is zero.
However as shown in FIG. 41, the back electromotive voltage (VBEMF) induced in the coils of the motor is raised as the motor rotating speed increases. At the maximum point of the motor rotating speed (4000 rpm in case of an eight-times speed CD-ROM, the back electromotive voltage (VBEMF) also reaches the maximum.
The current flowing in the coils of the motor at this moment is shown in FIG. 36 CASE 2!. The current IL flows via the same current path as shown in FIG. 35.
FIG. 37 and FIG. 38 show two stages of the decelerating mode. As shown in FIG. 41, since the motor control signal (EC) is higher than the reference voltage (ECR), the respective power-supply side and the earth side output power transistors 1.about.6 are on/off controlled so that a reverse torque is generated in the motor.
The following equation (1) is satisfied immediately after the mode is switched to the decelerating mode. The power-supply side output power transistor 2 and the earth side output power transistor 4 are controlled so that they turn on and the rest of the transistors turn off. EQU Rs.times.IL+VCE2+Ra.times.IL-VBEMF&lt;-Vd (1)
In a section where the condition of the equation (1) is satisfied, the current IL flows from the coil (resistance value Ra) of motor via the output node U, the earth side output power transistor 4, the detection resistor (resistance value Rs), the parasitic transistor 8, and the output node V, and back to the motor coil again, as shown in FIG. 37 CASE 3!, where the back electromotive force (VBEMF) is getting consumed.
The current IL at this time, takes a predetermined threshold current value (LIMIT decided by the motor driving circuit. Since the current IL is controlled to the limited current value, namely, the constant current state, the VCE 2 of the earth side output power transistor 4 is not saturated. Accordingly, the power consumption by the current IL is large.
As the current flows in this way and the back electromotive force (VBEMF) is consumed, the condition of the following equation (2) is satisfied. EQU Rs.times.IL+VCE2+Ra.times.IL-VBEMF&gt;-Vd (2)
When the condition of the equation (2) is satisfied, the current path through which current flows via the parasitic diodes 8 is intercepted. The regenerative current of the back electromotive force (VBEMF) flows as shown in FIG. 37 CASE 4!.
In other words, the current IL flows from the power supply 15 via the power-supply electric potential node Vcc, the power-supply side output power transistor 2, the output node V, the coil (resistance value Ra) of the motor, the output node U, the earth side output power transistor 4, the detection resistor (resistance value Rs), and the earth electric potential node GND, and backs to the power supply 15, where the back electromotive force (VBEMF) is getting consumed.
The power-supply side output power transistor 2 is not saturated as same as the CASE 3! shown in FIG. 37. Besides, since the electric potential of the emitter electrode of the earth side output power transistor 4 connected in parallel with the parasitic diodes 8 is close to the earth electric potential, the inter-collector-emitter voltage VCE 3 of the power-supply side output power transistor 2 takes a value close to the power supply voltage Vcc. Accordingly, the power consumption by the VCE 3 and the current IL reaches a considerably large amount of value as shown in the decelerating mode in FIG. 41.
This state is continued until the motor rotating speed is decelerated to a desired rotating speed. Even if this desired rotating speed reaches the minimum (1600 rpm in case of eight-times speed CD-ROM), this regenerative current IL continues to flow until the deceleration is terminated as that shown in FIG. 39 CASE 5!, as the same path as shown in FIG. 39 CASE 4!. As a result, a considerable amount of heat is generated in the motor driving circuit.
The above-mentioned brake system is generally called a reverse rotation brake. As shown in FIG. 40 CASE 6!, when the acceleration is started after the termination of the deceleration, the state becomes the same as that shown in FIG. 35 CASE 1!.
However, a large amount of electric power is consumed in the motor driving circuit constructed in this way due to the reverse rotation brake during the decelerating mode, and a considerable amount of heat is generated.
The heat constitutes a problem especially for a package, when this motor driving circuit is integrated into a semiconductor integrated circuit.
FIG. 41 shows a result of power consumption in the motor driving circuit measured under the severest heat condition (full stroke accelerating/decelerating) in case the motor driving circuit is applied to a reproducing equipment comprising an eight-times speed CD-ROM, for example. It is evident from FIG. 41 that the power consumption is considerably large as much as 5.about.10 (W) in the decelerating period, especially during the section CASE 4!.about.CASE 5! shown in FIG. 38 and FIG. 39, respectively.
The heat generated as a result of this amount of the power consumption constitutes a problem for a package in case the circuit is integrated into a semiconductor integrated circuit.
An object of the present invention is to reduce power consumption in the motor decelerating period, which reduces thermal effect and obtains a suitably integrated driving circuit in the semiconductor integrated circuit, for the driving circuit for driving a spindle motor (brushless motor) to rotate a recording medium when data is recorded or read out thereon at a constant line density.
It is another object of the present invention to provide a motor driving circuit which is able to control current flow during the decelerating period.
It is still another object of the present invention to provide a motor driving circuit to reduce power consumption, which reduces thermal effect and obtains a suitably integrated driving circuit in the semiconductor integrated circuit, without lengthening the seek time and the time necessary for stopping the motor during the decelerating period.
It is still further object of the invention to provide a motor driving circuit suitably made for being integrated into a semiconductor integrated circuit, which is characterized in that power consumption and thermal effect are decreased using a simple circuit configuration.